Gas sensor incorporating a porous framework

ABSTRACT

The disclosure provides sensor for gas sensing including CO 2  gas sensors comprising a porous framework sensing area for binding an analyte gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/142,564, filed on Jun. 28, 2011 (now U.S. Pat. No. 8,480,955),which is a U.S. National Stage Application filed under 35 U.S.C. §371,based upon International Application No. PCT/US09/69700, filed Dec. 29,2009, which claims priority under 35 U.S.C. §119 from ProvisionalApplication Ser. No. 61/141,200, filed Dec. 29, 2008, the disclosures ofwhich are incorporated herein by reference.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

This invention was made with Government support of Grant No.DEFG-02-08ER-15935 awarded by the Department of Energy. The Governmenthas certain rights in this invention.

The subject matter of this application arises in part from a jointresearch agreement between the Regents of the University of Californiaand BASF SE.

TECHNICAL FIELD

The disclosure provides sensor for gas sensing including CO₂ gas sensorscomprising a porous framework sensing area for binding an analyte gas.

BACKGROUND

Developing a simple, low cost CO₂ sensor is a goal that continues to beattempted with limited success. Carbon dioxide is very stable and hardto catalyze into ionic groups which could then be used for simpleconductometric detection. Current methods for CO₂ detection consist of:

(i) non-dispersive infrared (NDIR) sensors having an infrared source, alight tube, an interference (wavelength) filter, and an infrareddetector. The gas is pumped or diffuses into the light tube, and theelectronics measures the absorption of the characteristic wavelength oflight (Advantages—Sensitivities of 20-50 PPM, selective to error lessthan 10% solid state giving a life-time up to 10 years;Disadvantages—Very costly, typical NDIR sensors are still in the$100-$1000 range, relatively large and bulky);

(ii) Chemical CO₂ gas sensors with sensitive layers based on polymer,polymer arrays, metal oxides and new nanomaterials such as nanotubes andnanowires have the principal advantage of very low energy consumptionand can be reduced in size to fit into microelectronic-base systems. Onthe downside, short- and long term drift effects as well as a rather lowoverall lifetime are major obstacles when compared with the NDIRmeasurement principle; and (iii) other methods include optical fiberbased sensors and MEMS based sensors.

SUMMARY

The disclosure provides porous, covalently linked (reticulated)materials, such as metal organic frameworks (MOFs) and covalently-linkedorganic frameworks (COFs) and Zeolitic imidazolate frameworks (ZIFs) ascomponent sensors.

The disclosure provides a sensor comprising a region of a porousframework wherein the region absorbs or adsorbs a gas analyte ofinterest; and a transducer that converts a change in the region to adetectable property thereby measuring a gas analyte that absorbs oradsorbs to the region. In one embodiment, the transducer is an optical,mechanical or electrical transducer. In one embodiment, the region of aporous framework comprises a MOF, IRMOF, ZIF or COF. In anotherembodiment, a region comprising a ZIF material comprises the generalstructure M-L-M, wherein M comprises a transition metal and L is alinking moiety, the linking moiety comprising a structure selected fromthe group consisting of I, II, III, or any combination thereof:

wherein A can be either C or N, wherein R5-R8 are present when A1 and A4comprise C, wherein R¹, R⁴ or R⁹ comprise a non-sterically hinderinggroup that does not interfere with M, wherein R², R³, R⁵, R⁶, R⁷, R⁸,R¹⁰, R¹¹, R¹² are each individually an alkyl, halo-cyano-nitro-, whereinwhen the linking group comprises structure III, R10, R11 and R12 areeach individually electron withdrawing groups, wherein a gas analyte isadsorbed to the ZIF material. In one embodiment, the R₁, R₄ and R₉ areindividually small group selected from the group consisting of H,methyl-, halo-, cyano-, and ethyl-. In another embodiment, R₁₀, R₁₁ andR₁₂ are each individually selected from the group consisting of anitro-, cyano-, fluoro- and chloro-group. In yet another embodiment, Lis an imidazolate or an imidazolate derivative. In one embodiment, theimidazolate or imidazolate derivative is selected from the groupconsisting of a substituted imidazolate; a benzimidazolate comprising amethyl-, nitro-, cyano, or chloro-group; an azabenzimidazolate; and anazabenzimidazolte wherein one or two carbon atoms on the benzimidazolateare replaced by nitrogen. In yet a further embodiment, L is selectedfrom the group consisting of IV, V, VI, VII, VIII, and IX:

The sensor material may comprise a zeolitic framework comprising aplurality of different transition metals. For example, the transitionmetal can be selected from the group consisting of Sc, Ti, V, Cr, Mn,Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Lu, Hf, Ta,W, Re, Os, Ir, Pt, Au, Hg, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg and Uub.In yet another embodiment, the zeolitic framework comprises a pluralityof different linking groups. In another embodiment, the transition metalincreases the cationic charge of the zeolitic framework compared to aframework lacking a transition metal thereby increasing gas selectivity.In yet another embodiment, the sensor is a CO₂ sensor. In anotherembodiment, the presence of an analyte (e.g., CO₂) is detected byoptical changes, resistance changes, or mass changes in the sensingregion.

The disclosure also provides a sensor array comprising a plurality ofdifferentially responsive sensors wherein at least one sensor comprisesa region of a porous framework wherein the region absorbs or adsorbs agas analyte of interest; and a transducer that converts a change in theregion to a detectable property thereby measuring a gas analyte thatabsorbs or adsorbs to the region. In one embodiment, the sensor arraycomprises a plurality of different sensors comprising different porousframeworks. In one embodiment, the array comprises a sensor having aregion comprising a MOF, IRMOF, ZIF or COF. In another embodiment, aregion comprising a ZIF material comprises the general structure M-L-M,wherein M comprises a transition metal and L is a linking moiety, thelinking moiety comprising a structure selected from the group consistingof I, II, III, or any combination thereof:

wherein A can be either C or N, wherein R⁵—R⁸ are present when A1 and A4comprise C, wherein R¹, R⁴ or R⁹ comprise a non-sterically hinderinggroup that does not interfere with M, wherein R², R³, R⁵, R⁶, R⁷, R⁸,R¹⁰, R¹¹, R¹² are each individually an alkyl, halo-cyano-nitro-, whereinwhen the linking group comprises structure III, R10, R11 and R12 areeach individually electron withdrawing groups, wherein a gas analyte isadsorbed to the ZIF material. In one embodiment, the R₁, R₄ and R₉ areindividually small group selected from the group consisting of H,methyl-, halo-, cyano-, and ethyl. In another embodiment, R₁₀, R₁₁ andR₁₂ are each individually selected from the group consisting of anitro-, cyano-, fluoro- and chloro-group. In yet another embodiment, Lis an imidazolate or an imidazolate derivative. In one embodiment, theimidazolate or imidazolate derivative is selected from the groupconsisting of a substituted imidazolate; a benzimidazolate comprising amethyl-, nitro-, cyano, or chloro-group; an azabenzimidazolate; and anazabenzimidazolte wherein one or two carbon atoms on the benzimidazolateare replaced by nitrogen. In yet a further embodiment, L is selectedfrom the group consisting of IV, V, VI, VII, VIII, and IX:

The sensor material may comprise a zeolitic framework comprising aplurality of different transition metals. For example, the transitionmetal can be selected from the group consisting of Sc, Ti, V, Cr, Mn,Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Lu, Hf, Ta,W, Re, Os, Ir, Pt, Au, Hg, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg and Uub.In yet another embodiment, the zeolitic framework comprises a pluralityof different linking groups. In another embodiment, the transition metalincreases the cationic charge of the zeolitic framework compared to aframework lacking a transition metal thereby increasing gas selectivity.In yet another embodiment, the sensor is a CO₂ sensor. In anotherembodiment, the presence of an analyte (e.g., CO₂) is detected byoptical changes, resistance changes, or mass changes in the sensingregion.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic depicting a sensor process and sensing material ofthe disclosure.

FIG. 2A-C shows gas adsorption isotherms and CO₂ capture properties ofZIFs. (A) The N₂ adsorption isotherms for heterolinked ZIF-68, 69, and70 at 77 K. P/P0, relative pressure; STP, standard temperature andpressure. (B) The CO₂ and CO adsorption isotherms for ZIF-69 at 273 K.For (A) and (B), the gas uptake and release are indicated by solid andopen symbols, respectively. (C) Breakthrough curves of a stream ofCO₂/CO mixture passed through a sample of ZIF-68 showing the retentionof CO₂ in the pores and passage of CO.

DETAILED DESCRIPTION

As used herein and in the appended claims, the singular forms “a,”“and,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a sensor” includesa plurality of such sensors and reference to “the transducer” includesreference to one or more transducers and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. Although any methods andreagents similar or equivalent to those described herein can be used inthe practice of the disclosed methods and compositions, the exemplarymethods and materials are now described.

Also, the use of “or” means “and/or” unless stated otherwise. Similarly,“comprise,” “comprises,” “comprising” “include,” “includes,” and“including” are interchangeable and not intended to be limiting.

It is to be further understood that where descriptions of variousembodiments use the term “comprising,” those skilled in the art wouldunderstand that in some specific instances, an embodiment can bealternatively described using language “consisting essentially of” or“consisting of.”

All publications mentioned herein are incorporated herein by referencein full for the purpose of describing and disclosing the methodologies,which are described in the publications, which might be used inconnection with the description herein. The publications discussed aboveand throughout the text are provided solely for their disclosure priorto the filing date of the present application. Nothing herein is to beconstrued as an admission that the inventors are not entitled toantedate such disclosure by virtue of prior disclosure.

The approach described herein uses porous framework materials that bindto an analyte gas of interest and which upon binding to the analyteundergo a detectable change that can be measure by a transducer therebyindicating the presence of an absorbed analyte. For example, thedisclosure provides porous frameworks that can be used in any number ofsensor modalities comprising different transducers for measuring adetectable signal. Chemically-sensitive resistor, for example, can beused wherein the sensing region comprises a porous framework of thedisclosure either alone or in combination with other conductive ornon-conductive materials. Such sensors can be used in a sensing array.The change in the electrical resistance of a chemically-sensitiveresistor in such a sensing array can be related to the sorption of amolecule of interest to the porous framework.

Other sensor modalities include acoustic wave, capacitance and opticaltransduction methods. Acoustic wave sensors measure an absorbed materialby change in the vibrational frequency of the sensor (e.g., a sensorcomprising a porous framework). For instance, an acoustic wave sensormay have a first vibrational frequency in the absence of a bound analyteand a second different frequency in the presence of the bound analyte.Measuring such changes in vibrational frequency can be performed in themethods and compositions of the disclosure wherein the sensor comprisesa porous framework and wherein the porous framework changes mass (thusvibrational frequency) when the material binds an analyte.

Similarly, the presence of a bound analyte can be measured optically. Inoptical transduction modalities the optical properties are measured inthe porous material prior to contact with an analyte and thensubsequence to contact with the analyte. Light diffusion through asensor material can be detected or a change in the color of the materialmay be detected.

Another type of sensor includes, for example, a sensor that undergoes avolume change in response to an analyte species. As the sensors aremodulated in size the sensor material changes with respect to mass oroptics. For example, the light diffraction indicates the presence orabsence of the analyte that causes the sensing material to change. Inthis embodiment, the sensor material comprises a porous sensor material(e.g., a MOF, IRMOF, COF, ZIF or a combination thereof) that can bespecifically functionalized for binding an analyte of interest eitherreversibly or irreversibly.

Yet another type of sensor includes those wherein the sensors produce aspectral recognition patterns when an analyte is present. In thisembodiment the porous sensor material changes in optical properties,whether by density or through a change in emission, excitation orabsorbance wavelengths.

Any number of sensor combinations comprising a porous framework of thedisclosure or any number of transduction modalities can be used. Forexample, each individual sensor can provide a signal (e.g., a transducedsignal indicative of the presence of an analyte) or a plurality ofsignals from an array of sensors can be used to identify an analyte ofinterest in a fluid. The signal transduction mechanism through which theanalyte or molecule produces a signal is potentially quite broad. Theseinclude arrays of surface acoustic wave devices, quartz crystalmicro-balances, dye-coated fiber optics, resistometric, electrochemical,and others modalities readily identifiable to those skilled in the art.Accordingly, transduction mechanisms include, for example optical,electrical, and/or resonance.

By “differentially responsive sensors” is meant any number of sensorscomprising a porous framework that respond (e.g., transducer a signal)to the presence or interaction of an analyte with the sensor. Suchmeasurable changes include changes in optical wavelengths, transparencyof a sensor, resonance of a sensor, resistance, diffraction of lightand/or sound, and other changes easily identified to those skilled inthe art.

The disclosure provides sensors comprising a metal organic framework(MOF), an iso-reticular metal organic framework (IRMOF), a covalentorganic framework (COF), a zeolitic inorganic framework (ZIF) or anycombination thereof (referred to herein as a “porous sensor material”).MOFs, IRMOFs, COFs, and ZIFs are porous frameworks that can befunctionalized to bind and interact with various analytes including, butnot limited to, ammonia, carbon dioxide, carbon monoxide, hydrogen,amines, methane, oxygen, argon, nitrogen, argon, organic dyes,polycyclic organic molecules, and combinations thereof. Such sensorsinclude, for example, chemically-sensitive resistor wherein the MOF,IRMOF, COF, and/or ZIF composition (porous sensor material) is disposedbetween conductive leads and undergoes a change in resistance when theporous material adsorbs or absorbs an analyte. The change in theelectrical resistance between the leads can be related to the sorptionof an analyte to the porous sensor material.

The diversity of the sensors of the disclosure comprising a porousframework material can be increased by combining the framework withadditional material (e.g., conductive polymers, insulators and thelike).

In one embodiment, the disclosure provides a sensing platform comprisinga sensing region of a metal organic frameworks (MOF). The framework is ahighly porous nanostructure that readily adsorb/desorb an analyte whichcan be sensed via various transducing methods.

Metal-organic frameworks (MOFs) are a class of crystalline porousmaterials whose structure is composed of metal-oxide units joined byorganic linkers through strong covalent bonds. MOF materials are porous,crystalline solids. They are composed of metal-coordination-polyhedra(SBUs) and ligands (linking moieties). The ligands are at leastbidentate to allow the formation of a one-, two- or three-dimensionalextended structure (e.g., a teraphthalic acid or imidazol). Thecoordination-polyhedron can contain one or more than one metal ions(e.g., Zn₄O-cluster or Cu₂-paddlewheel). MOFs are described in moredetail elsewhere herein.

The flexibility with which these components can be varied has led to anextensive class of MOF structures with ultra-high surface areas, farexceeding those achieved for porous carbons. MOFs exhibit high thermalstability, with decomposition between 350° C. and 400° C. in the case ofMOF-5 (Eddaoudi M, et al., Science 295:469-472, 2002), ensuring theirapplicability across a wise temperature range. The unprecedented surfacearea and the control with which their pore metrics and functionality canbe designed provides limitless potential for their structure to betailored to carry out a specific application.

The ZIF family of materials follows the same building principles but theligands are chose from organic molecules with imidazolate moieties(e.g., imdazolate, benzimidazolate, adenine, cytosine and so on), themetal coordination polyhedra typically contains one metal ion (e.g.,Zinc(II)) and is a tetrahedron. These materials resemble topologiesfound in inorganic zeolites and are able to generate topologies whichwere not yet observed in inorganic zeolites. One feature that makes thisclass of material a useful sensor composition is its stability towards avast variety of solvents, including water, and its stability even underharsh conditions (e.g., hot NaOH-solution (8M NaOH(aq))).

A zeolitic frameworks can comprise a network of homogenous transitionmetal or heterogeneous transition metals linked by a homogenous orheterogeneous linking moiety. The zeolitic frameworks of the disclosurecan comprise any of the networks currently defined in the Atlas ofZeolite Structure Types known in the literature as well as POZ. Thezeolitic frameworks of the disclosure provide nanoporous structureuseful for filtration, gas storage and the like, as more fully describedherein.

The disclosure also provide a general synthesis of structures havingzeolite framework topologies in which all tetrahedral atoms aretransition metals, and the linking moieties comprise organic linkerscomprising nitrogen, sulfur or oxygen organic molecules (e.g., such asimidazolate (IM) units). The organic linkers may be furtherfunctionalized to modify the cage size and pore size or specificity to aguest species or gas molecule.

Zeolitic frameworks comprise the general structure M-L-M, wherein Mcomprises a transition metal and L is a linking moiety, wherein theframework is selected from the group consisting of:

(a) M-L-M, wherein L comprises structure I, II, or III; and

(b) M-L-M, wherein at least one L is structure II or III and at leastone other L is a structure I, II or a combination thereof:

wherein A can be either C or N, wherein R⁵—R⁸ are present when A¹ and A⁴comprise C, wherein R¹, R⁴ or R⁹ comprise a non-sterically hinderinggroup that does not interfere with M, wherein R², R³, R⁵, R⁸, R¹⁰, R¹¹,R¹² are each individually an alkyl, halo-cyano-nitro-, wherein when thelinking moiety comprises structure III, R¹⁰, R¹¹ and R¹² are eachindividually electron withdrawing groups, and wherein one of R⁶ and R⁷comprise an electron withdrawing group.

In one embodiment, R¹, R⁴ or R⁹ comprise a non-sterically hinderingelectron donating group that does not interfere with M. The R¹, R⁴ or R⁹functionalized with a group selected to interact with a particular gasor substrate. In another embodiment, R², R³, R⁶, R⁷, or R¹¹ areindividually H or a small electron withdrawing group. In one embodiment,the small electron withdrawing group is of sufficient size to increase acage size for a ZIF of the disclosure. For example, R⁷ can be achloro-group.

In a further embodiment the imidazolate or imidazolate derivative isselected from the group consisting of IV, V, VI, VII, VIII, and IX:

In one embodiment, the imidazolate or imidazolate derivative is selectedfrom the group consisting of a substituted imidazolate; abenzimidazolate comprising a methyl-, nitro-, cyano, or chloro-group; anazabenzimidazolate; and an azabenzimidazolate wherein one or two carbonatoms on the benzimidazolate are replaced by nitrogen. The transitionmetal is selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe,Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Lu, Hf, Ta, W,Re, Os, Ir, Pt, Au, Hg, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg and Uub. Inone embodiment, a zeolitic framework comprises a heterogeneouscombination of transition metals. In yet another embodiment, thezeolitic framework comprises homogenous transition metal but aheterogeneous combination of linking moieties. In a further embodiment,a zeolitic framework comprises a heterogeneous mixture of transitionmetals and linking moieties.

In yet another embodiment, the linking moiety comprises abenzimidazolate (bIM) functionalized at the 5 or 4 and 5 positions tomodify the pore character and/or cage structure of the framework. Thefunctionalization moiety is used to increase the IM girth and comprisesa small electron withdrawing group. The functionalization moiety cancomprise, for example, a chloro-, bromo-, iodo-, or fluoro-containinggroup. For example, the disclosure provides a 5-chlorobenzimidazolate(cbIM) linked to a transition metal selected from the group consistingof Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd,Ag, Cd, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Lr, Rf, Db, Sg, Bh, Hs,Mt, Ds, Rg and Uub. In one embodiment, the cbIM linking moiety is linkedto a Zn or Co transition metal.

In one embodiment, the imidazolate or imadazolate derivative linkingmoiety (metal groups not depicted) has a structure selected from thegroup consisting of:

An isoreticular metal-organic framework (IRMOF) according to thedisclosure comprises a plurality of secondary building units (SBUs),each of the plurality of SBUs comprises, for example, an M₄O(CO₂)₆cluster. A compound links adjacent SBUs, the linking compound comprisinga linear ditopic carboxylate having at least one phenyl group and atleast one functional group X attached to at least one phenyl group. TheIRMOF formed has substantial permanent porosity and is very stable, withor without the presence of guest molecules.

M in the SBU is a metal cation. For example, the metal cation can beselected from the group consisting of a beryllium, zinc, cadmium,mercury, and any of the transition metals (in the periodic table,scandium through copper, yttrium through silver, lanthanum through gold,and all known elements from actinium on).

Particularly the MOF or IRMOF comprises a reactive side group, X, thatcan bond (either covalently, ionically or through hydrogen bonds with agas analyte). In one embodiment the reactive side group is a Lewis Acidor base group.

Coordinatively unsaturated metal sites (e.g., MOF-74 and MOF-199) andamino functionality (e.g., IRMOF-3) prove effective in adsorbinganalytes that interact strongly with those groups. For example, MOF-199demonstrates efficacy equal to or greater than BPL-carbon against allgases and vapors tested except chlorine. It is particularly effective inremoving gases that are vexing for activated carbons such as ammonia andethylene oxide.

It is clear that a successful MOF-based dynamic adsorption medium willcontain some reactive functionality, often in the form of acoordinatively unsaturated metal site. A variety of MOFs with reactivefunctionality in the pores is known; and there exists immense potentialfor the development of new MOFs with untested functionalities andmetals. Furthermore, the performance of any MOF stands to be improveddramatically once it is impregnated with reactive ions and compounds.

Such porous covalently linked (reticulated) materials have in commonthat the properties of the pores can be precisely tuned to match theprerequisites for a given analyte. Tuneable properties include, but arenot limited to, pore size, pore volume, polarity, magnetic properties,chemical environment (e.g., functional groups, metal coordinationsites), and geometry of binding sites (e.g., introducing pockets for theanalyte and the like.

Carbon dioxide, for example, as an analyte, interacts selectively withthe ions of the SBU or with functional groups on the linker (e.g., NH₂).This interaction is selective or can be designed to be selective for oneanalyte versus another. For example, the CO₂ may be selectively absorbedor adsorbed to a porous framework of the disclosure while other analytes(e.g., CO, N₂, O₂, NO, NO₂, Ar, C_(x)H_(y), benzene and the like) arenot. For example, ZIF-69 is selective for capture of carbon dioxide.Such behaviour has relevant applications as a very specific andsensitive CO₂ sensor.

Generally, a useful sensing material comprising an organic frameworks ofthe disclosure have the general structure M-L-M, wherein L is a linkingmoiety and M are transition metals or mono- or poly-dentate groupscapable of linking to at least one other linking moiety. The disclosuretakes advantage of the modification of exposed side-group on a linkingmoiety (in some embodiments post synthesis), that can be reactive withan analyte of interest or functionalized by, for example, a post framework reactant under suitable reaction conditions.

As used herein, a “core” refers to a repeating unit or units found in aframework. Such a framework can comprise a homogenous repeating core ora heterogeneous repeating core structure. A core comprises a transitionmetal or cluster of transitions metals and a linking moiety. A pluralityof cores linked together defines a framework.

The term “cluster” refers to identifiable associations of 2 or moreatoms. Such associations are typically established by some type ofbond-ionic, covalent, Van der Waal, and the like.

A “linking cluster” refers to a one or more reactive species capable ofcondensation comprising an atom capable of forming a bond between alinking moiety substructure and a metal group or between a linkingmoiety and another linking moiety. Examples of such species are selectedfrom the group consisting of a boron, oxygen, carbon, nitrogen, andphosphorous atom. In some embodiments, the linking cluster may compriseone or more different reactive species capable of forming a link with abridging oxygen atom. For example, a linking cluster can comprise CO₂H,CS₂H, NO₂, SO₃H, Si(OH)₃, Ge(OH)₃, Sn(OH)₃, Si(SH)₄, Ge(SH)₄, Sn(SH)₄,PO_(S)H, AsO₃H, AsO₄H, P(SH)₃, AS (SH)₃, CH(RSH)₂, C(RSH)₃, CH(RNH₂)₂,C(RNH₂)₃, CH(ROH)₂, C(ROH)₃, CH(RCN)₂, C(RCN)₃, CH(SH)₂, C(SH)₃,CH(NH₂)₂, C(NH₂)₃, CH(OH)₂, C(OH)₃, CH(CN)₂, and C(CN)₃, wherein R is analkyl group having from 1 to 5 carbon atoms, or an aryl group comprising1 to 2 pheny rings.

The term “covalent organic polyhedra” refers to a non-extended covalentorganic network. Polymerization in such polyhedra does not occur usuallybecause of the presence of capping ligands that inhibit polymerization.Covalent organic polyhedra are covalent organic networks that comprise aplurality of linking clusters linking together multidentate cores suchthat the spatial structure of the network is a polyhedron. Typically,the polyhedra of this variation are 2 or 3 dimensional structures.

A “linking moiety” refers to a mono-dentate or polydentate compound thatbind a transition metal or a plurality of transition metals,respectively. Generally a linking moiety comprises a substructurecovalently linked to an alkyl or cycloalkyl group, comprising 1 to 20carbon atoms, an aryl group comprising 1 to 5 phenyl rings, or an alkylor aryl amine comprising alkyl or cycloalkyl groups having from 1 to 20carbon atoms or aryl groups comprising 1 to 5 phenyl rings, and in whicha linking cluster (e.g., a multidentate function groups) are covalentlybound to the substructure. A cycloalkyl or aryl substructure maycomprise 1 to 5 rings that comprise either of all carbon or a mixture ofcarbon with nitrogen, oxygen, sulfur, boron, phosphorus, silicon and/oraluminum atoms making up the ring. Typically the linking moiety willcomprise a substructure having one or more carboxylic acid linkingclusters covalently attached.

As used herein, a line in a chemical formula with an atom on one end andnothing on the other end means that the formula refers to a chemicalfragment that is bonded to another entity on the end without an atomattached. Sometimes for emphasis, a wavy line will intersect the line.

In one embodiment, the linking moiety substructure is selected from anyof the following:

wherein R₁, R₂, R₃, R₄═NH₂, CN, OH, ═O, ═S, SH, P, Br, CL, I, F,

wherein X=1, 2, or 3. Further examples of ZIFs, MOFs, COFs and BOFs areset forth herein.

In one embodiment, the linking moiety of the disclosure can comprisesubstituted or unsubstituted aromatic rings, substituted orunsubstituted heteroaromatic rings, substituted or unsubstitutednonaromatic rings, substituted or unsubstituted nonaromatic heterocyclicrings, or saturated or unsaturated, substituted or unsubstituted,hydrocarbon groups. The saturated or unsaturated hydrocarbon groups mayinclude one or more heteroatoms. For example, the linking moietysubstructure can comprise Formula XI:

wherein R₁, R₂, R₃, and R₄ are each independently H, alkyl, aryl, OH,alkoxy, alkenes, alkynes, phenyl and substitutions of the foregoing,sulfur-containing groups (e.g., thioalkoxy), silicon-containing groups,nitrogen-containing groups (e.g., amides), oxygen-containing groups(e.g., ketones, and aldehydes), halogen, nitro, amino, cyano,boron-containing groups, phosphorus-containing groups, carboxylic acids,or esters.

In one embodiment, the linking group comprises a structure selected fromthe group consisting of:

wherein the carboxylic acid groups above undergo a condensation with atransition metal to form a framework and wherein R₁, R₂, R₃, R₄═NH₂, CN,OH, ═O, ═S, SH, P, Br, CL, I, F,

wherein X=1, 2, or 3.

In another variation of the linking moiety is described by Formula XII:

wherein R₁, R₂, R₃, R₄, R₅, and R₆ are each independently H, alkyl,aryl, OH, alkoxy, alkenes, alkynes, phenyl and substitutions of theforegoing, sulfur-containing groups (e.g., thioalkoxy),silicon-containing groups, nitrogen-containing groups (e.g., amides),oxygen-containing groups (e.g., ketones, and aldehydes), halogen, nitro,amino, cyano, boron-containing groups, phosphorus-containing groups,carboxylic acids, or esters. In one embodiment, R₁, R₂, R₃, R₄ are eachindependently selected from the group consisting of NH₂, CN, OH, ═O, ═S,SH, P, Br, CL, I, F,

wherein X=1, 2, or 3.

In another variation the linking moiety is described by FormulaXIII-XVI:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄,R₁₅, and R₁₆ are each independently H, alkyl, aryl, OH, alkoxy, alkenes,alkynes, phenyl and substitutions of the foregoing, sulfur-containinggroups (e.g., thioalkoxy), silicon-containing groups,nitrogen-containing groups (e.g., amides), oxygen-containing groups(e.g., ketones, and aldehydes), halogen, nitro, amino, cyano,boron-containing groups, phosphorus-containing groups, carboxylic acids,or esters and T is a tetrahedral atom (e.g., carbon, silicon, germanium,tin) or a tetrahedral group or cluster. In one embodiment, R₁, R₂, R₃,R₄ are each independently selected from the group consisting of NH₂, CN,OH, ═O, ═S, SH, P, Br, CL, I, F,

wherein X=1, 2, or 3.

In another variation the linking moiety is described by Formula XVII:

wherein A₁, A₂, A₃, A₄, A₅, and A₆ are each independently absent or anyatom or group capable of forming a sable ring structure and R₁, R₂, R₃,R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are each independently H,alkyl, aryl, OH, alkoxy, alkenes, alkynes, phenyl and substitutions ofthe foregoing, sulfur-containing groups (e.g., thioalkoxy),silicon-containing groups, nitrogen-containing groups (e.g., amides),oxygen-containing groups (e.g., ketones, and aldehydes), halogen, nitro,amino, cyano, boron-containing groups, phosphorus-containing groups,carboxylic acids, or esters. In one embodiment, R₁, R₂, R₃, R₄ are eachindependently selected from the group consisting of NH₂, CN, OH, ═O, ═S,SH, P, Br, CL, I, F,

wherein X=1, 2, or 3. Specific examples of Formula XVII are provided byFormulae XVIII and XIX and ammonium salts of the linking groups ofFormulae XVIII and XIX:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are eachindependently H, alkyl, aryl, OH, alkoxy, alkenes, alkynes, phenyl andsubstitutions of the foregoing, sulfur-containing groups (e.g.,thioalkoxy), silicon-containing groups, nitrogen-containing groups(e.g., amides), oxygen-containing groups (e.g., ketones, and aldehydes),halogen, nitro, amino, cyano, boron-containing groups,phosphorus-containing groups, carboxylic acids, or esters. In oneembodiment, R₁, R₂, R₃, R₄ are each independently selected from thegroup consisting of NH₂, CN, OH, ═O, ═S, SH, P, Br, CL, I, F,

wherein X=1, 2, or 3.

In yet another variation the linking moiety is described by Formula XX:

wherein R₁ through R₁₂ are each independently H, alkyl, aryl, OH,alkoxy, alkenes, alkynes, phenyl and substitutions of the foregoing,sulfur-containing groups (e.g., thioalkoxy), silicon-containing groups,nitrogen-containing groups (e.g., amides), oxygen-containing groups(e.g., ketones, and aldehydes), halogen, nitro, amino, cyano,boron-containing groups, phosphorus-containing groups, carboxylic acids,or esters; and n is an integer greater than or equal to 1. In oneembodiment, R₁, R₂, R₃, R₄ are each independently selected from thegroup consisting of NH₂, CN, OH, ═O, ═S, SH, P, Br, CL, I, F,

wherein X=1, 2, or 3.

The interaction of the analyte with the framework results in the changeof the physical properties of the material. Changes can be observed inmass, conductivity, optical properties and magnetic properties (see,e.g., FIG. 1). For example, the mass of a MOF increases as more CO₂ iscaptured. For instance, ZIF-69 can hold up to 12 weight percent of CO₂at room temperature and pCO₂=1bar. This represents an increase in massof nearly 90 grams. Such changes represent an extremely large signalchange to gravimetric sensors that have sensitivity in the nanograms andpictogram ranges.

Optical properties of CO₂ absorption can be detected by infraredradiation. For example, CO₂ absorbs infrared wavelength radiation at 1.4microns. Therefore by passing IR radiation through a porous framework ofthe disclosure a signal that is inversely proportional to CO₂concentration can be obtained.

Conductivity measurements can also be used in the sensors of thedisclosure. For example, capture of CO₂ within the metal organicframework alters the electronic properties of the framework. Due to CO₂increasing the density of the material and enabling electron carriertransport and aggregate conductivity of a MOF increases.

A porous material of the disclosure is used as the sensing materialeither alone or as a combination with inorganic materials, organicmaterials, conductive materials (e.g., inorganic conductors or organicconductors), polymers (e.g., conductive or non-conductive polymers). Theporous materials (e.g., MOF material) of the disclosure can be combinedwith other materials for purposes of sensing as mixtures or suspensionthat can then be layered at varying thickness on a substrate.

For example, MOFs for use in mass sensing can be used with quartzcrystal microbalances, surface acoustic wave sensors and MEMScantilevers. Conductometric transducers such as interdigtial electrodetransducers can be used or optical transducers such as those comprisingan optical path with a source and detector separated by the poroussensing material of the disclosure.

ZIF materials are transparent to light in the region between 2000 and25000 cm⁻¹. CO₂ absorbs IR-light in this region. The optical NDIRsensors for CO₂ make use of that absorption to quantify the CO₂ contentof a gas mixture. The ZIF materials can be used as an extra layer toincrease the partial pressure of CO₂ by adsorption of CO₂ in theframework in the optical path of the sensor setup this layer acts as anamplifier (see e.g., Table 1).

TABLE 1 p(CO₂) partial pressure of CO₂ in the gas phase; p′(CO₂):virtual partial pressure in the pore system; amplification:p′(CO₂)/p(CO₂); p(CO₂)/mbar p′(CO₂)/mbar amplification CO₂/wt % 3.0747.7 155 0.01% 30.4 461   152 0.09% 150 18.0 · 10³ 120 3.30% 298 31.2 ·10³ 105 5.60% 996 70.6 · 10³ 70.6 11.8%Furthermore the adsorbed gas results in an increase in weight which canbe measured by a QCM set up. Due to the high capacity for CO₂, thisweight increase is larger than for other materials and the uptake isreversible.

The porous materials described herein serve as effective adsorptionmedium for gas sensing and more particularly CO₂ sensing having longterm viability and combine two features: (i) a periodic structure forwhich carbon dioxide uptake and release is fully reversible, and (ii) aflexibility with which chemical functionalization and molecular levelfine-tuning can be achieved for optimized uptake capacities.

The analysis of change in sensor composition (e.g., due to binding of ananalyte) measured by a change in, for example, resistance, mass oroptical properties may be implemented in hardware or software, or acombination of both (e.g., programmable logic arrays and digital signalprocessors). Unless otherwise specified, the algorithms included as partof the disclosure are not inherently related to any particular computeror other apparatus.

In particular, various general purpose machines may be used withprograms written in accordance with the teachings herein, or it may bemore convenient to construct more specialized apparatus to perform theoperations. However, preferably, the embodiment is implemented in one ormore computer programs executing on programmable systems each comprisingat least one processor, at least one data storage system (includingvolatile and non-volatile memory and/or storage elements), at least oneinput device, and at least one output device. The program code isexecuted on the processors to perform the functions described herein.

Each such program may be implemented in any desired computer language(including machine, assembly, high level procedural, or object orientedprogramming languages) to communicate with a computer system. In anycase, the language may be a compiled or interpreted language.

Each such computer program is preferably stored on a storage media ordevice (e.g., ROM, CD-ROM, or magnetic or optical media) readable by ageneral or special purpose programmable computer, for configuring andoperating the computer when the storage media or device is read by thecomputer to perform the procedures described herein. The system may alsobe considered to be implemented as a computer-readable storage medium,configured with a computer program, where the storage medium soconfigured causes a computer to operate in a specific and predefinedmanner to perform the functions described herein.

For example, the computer can be used to measure a signal from thesensor and output an indication of the present of a gas or analyte. Insome embodiments, the output may be transmitted to a remote location.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method of detecting an analyte in a fluidcomprising contacting the analyte with a sensor comprising a region of aporous framework wherein the region absorbs or adsorbs a gas analyte ofinterest; and a transducer in electrical, mechanical or opticalcommunication with the region that converts an electrical, optical ormass change in the region to a detectable property thereby measuring agas analyte that absorbs or adsorbs to the region, and measuring achange in the detectable property thereby detecting the analyte.
 2. Themethod of claim 1, wherein the analyte is CO₂.
 3. The method of claim 1,wherein the transducer is an optical, mechanical or electricaltransducer.
 4. The method of claim 1, wherein the region comprises ametal organic framework (MOF), isoreticular metal organic framework(IRMOF), zeolitic imidazolate framework (ZIF) or covalent organicframework (COF).
 5. The method of claim 4, wherein the region comprisesa ZIF-68, ZIF-69 or ZIF-70 framework.
 6. The method of claim 4, whereinthe ZIF comprises the general structure M-L-M, wherein M comprises atransition metal and L is a linking moiety, the linking moietycomprising a structure selected from the group consisting of I, II, III,or any combination thereof:

wherein, A can be either C or N; R⁵—R⁸ are present when A¹ and A⁴comprise C; R¹, R⁴ or R⁹ comprise a non-sterically hindering group thatdoes not interfere with M; and R², R³, R⁵, R⁶, R⁷, R⁸, R¹⁰, R¹¹, R¹² areeach individually an alkyl, halo, cyano, or nitro, wherein when thelinking group comprises structure III, R¹⁰, R¹¹ and R¹² are eachindividually electron withdrawing groups, and wherein a gas analyte isadsorbed to the zeolitic framework.
 7. The method of claim 6, whereinR¹, R⁴ and R⁹ are individually small group selected from the groupconsisting of H, methyl, halo, cyano, and ethyl.
 8. The method of claim6, wherein R¹⁰, R¹¹ and R¹² are each individually selected from thegroup consisting of a nitro, cyano, fluoro and chloro group.
 9. Themethod of claim 6, wherein L is selected from the group consisting ofIV, V, VI, VII, VIII, and IX:


10. The method of claim 6, wherein the zeolitic framework comprises aplurality of different transition metals.
 11. The method of claim 6,wherein the zeolitic framework comprises a plurality of differentlinking groups.
 12. The method of claim 6, wherein the transition metalis selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni,Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Lu, Hf, Ta, W, Re, Os,Ir, Pt, Au, Hg, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg and Uub.
 13. Themethod of claim 6, wherein the transition metal comprises a metal thatincreases the cationic charge of the zeolitic framework therebyincreasing gas selectivity.
 14. The method of claim 6, wherein L is animidazolate or an imidazolate derivative.
 15. The method of claim 14,wherein the imidazolate or imidazolate derivative is selected from thegroup consisting of a substituted imidazolate; a benzimidazolatecomprising a methyl, nitro, cyano, or chloro group; anazabenzimidazolate; and an azabenzimidazolte wherein one or two carbonatoms on the benzimidazolate are replaced by nitrogen.